The tensioning devices are capable of exerting an axial tensile force to one end of a threaded rod by means of a tie-rod. The device rests on a surface of a structure to be tightened by means of a tubular support sleeve surrounding an end of the threaded rod. The device provides a cylinder and a piston sliding in the cylinder and forming with the cylinder an annular chamber dedicated to be fed with pressurized fluid.
The rod is tensioned by means of the piston pressurized and is stretched. The rod is then locked by means of a nut for example, directly on the rod or on the device itself. The released rod tends to recover its resting length but is blocked by the nut. The released rod then exerts a tightening force on the mechanical parts to tighten. Such tightening method is an advantageous alternative to tightening a nut to which an important tightening torque is to be applied.
However, such known tensioning devices are designed to be fed by a fluid under pressure up to 1,500 bar. But in some applications of reduced space, the exerted force is not enough to maintain the mechanical structures tightened together.
Furthermore, elements of the device are axially assembled but have radial overlap portions for both the retention and the sealing under fluid pressure. In some applications, the available space is greatly reduced and such devices cannot be used.